For bacon potato salad with fried fish first boil pell potatoes. For the marinade season vinegar with sugar, pepper and salt. Finely dice and add the onions. Bring the stock to the boil and pour hot over the onions. Peel the potatoes, cut into slices and mix into the marinade. In a frying pan let out butter. Fry the diced bacon until crispy and add to the salad. Leave bacon potato salad to stand for at least 30 minutes. For the roast fish, rinse the red perch fillet and pat dry. Season with salt and pepper. Turn fried fish in flour, then in whisked egg and finally in breadcrumbs flour. Heat the fat in a pan. Fry the fish briefly on both sides. Reduce heat. Roast fish 5 minutes per side. Serve with bacon potato salad.